Electromagnetically steered microwave antenna



Sept. 22, 1959 E. e. SPENCER ETAL 2,905,940

ELECTROMAGNETICALLY STEERED MICROWAVE ANTENNA Filed May 2, 1957 2Sheets-Sheet.1

INPU 7' JEW L lib- I INVENTORS Edward G.Spencer Frank Reggie BY John E.Tompkins Robert D.Hotcher r. 5%, 1.4%, wWM/ W Sept. 22, 1959 E. G.SPENCER ETAL 2,905,940

ELECTROMAGNETICALLY STEERED MICROWAVE ANTENNA Filed May 2, 1957 2Sheets-Sheet 2 om mum um llll l HHNUIIJ. 6.0

INVENTOR Edward G.Spe ncer Frank Reggie BY John E. Tompkin Robert D.Hmcher QN I nited States Patent Ofiice 2,905,940 Patented Sept. 22, 1959ELECTROMAGNETICALLY STEERED MICROWAVE ANTENNA Edward G. Spencer,Rockville, Frank Reggia, Chevy Chase, and John E. Tompkins, Bethesda,Md., and Robert D. Hatcher, Washington, D.C., assignors to the UnitedStates of America as represented by the Secretary of the ArmyApplication May 2, 1957, Serial No. 656,733-

8 Claims. (Cl. 343-778) (Granted under Title 35, U.S. Cde (1952), sec.266) V The invention described herein may be manufactured and used by orfor the Government for governmental purposes without the payment to usof any royalty there- This invention relates to the electrical controlof microwave structures in general and more particularly to microwavecavity means for electrically varying the microwave length along amicrowave structure at a predetermined place.

In preferred forms of the invention, variations in the electrical lengthat microwave frequencies, along a microwave structure are obtained byelectrically varying the resonant frequency of a resonant microwavecavity coupled to the microwave structure at the place where the changein microwave length is desired. The resonant microwave cavity may beexternal to the microwave structure or else may be internal, that is theresonant microwave cavity may be an elementary resonant cavity formingpart of the microwave structure. By resonant cavity is meant a cavity ina system having an operating frequency approximately equal to theresonant frequency of the cavity. Because small changes in the resonantfrequency of such a resonant cavity produce large changes in thereactance presented by the cavity, large variations in microwave lengthare obtained at the place of coupling. These large variations inmicrowave length may be advantageously used in microwave antenna arrays.By varying the microwave length between two radiators, the phase of theenergy radiated by one radiator can be varied relative to the phase ofthe energy radiated by the other radiator.

One object of the invention is to provide improved microwave controlmeans for electrically varying the microwave length along a microwavestructure at a predetermined place.

Another object is to provide improved means for varying the resonantfrequency of a resonant microwave cavity.

A further object is to provide improved microwave antenna arrays havingelectrically controlled means for rapidly and conveniently varying thephases between the energy radiated by the radiators relative to oneanother.

A further object of this invention is to provide improved microwaveantenna arrays having electrically controlled means for varying thephases between the energy radiated by the radiators relative to oneanother over considerably larger ranges than heretofore obtainable.

Still another object is to provide improved means for exciting andcontrolling the power radiated by microwave radiating elements.

The specific nature of the invention as well as other objects, uses andadvantages thereof will clearly appear from the following descriptionand from the accompanying drawing, in which:

Figure 1 is a simplified sectional and schematic representation of awaveguide-fed linear array having external microwave cavity means forelectrically varying the relative phase between the energy radiated bythe radiators, in accordance with the invention.

Figure 2a shows a cavity-fed linear array having internal microwavecavity means for electrically varying the relative phase between theenergy radiated by the radiators, in accordance with the invention.

Figure 2b is a cross-sectional view taken along the line 2b2b of Figure2a.

Figure 3a shows a rectangular cavity-fed array having internal microwavecavity means for electrically varying the phases between the energyradiated by the radiators relative to one another, in accordance withthe invention.

Figure 3b is a cross-sectional view taken along the line 3b3b of Figure3a.

Figure 4a is a top view of a rectangular cavity-fed array havingexternal microwave cavity means for electrically varying the phasesbetween the energy radiated by the radiators relative to one another, inaccordance with the invention.

Figure 4b is a front view of Figure 4a.

In Figure 1, a section of waveguide 12 is adapted to be supplied withmicrowave energy at one end 14 and is terminated in a matching impedance16 at the other end 18.

Two ferrite radiating elements 20a and 20b are placed to form a lineararray and are coupled to the waveguide 12 in accordance with well knownpractice.

A resonant cavity 24 is coupled to the waveguide 12 at a placeintermediate to the radiators 20a and 20b by coincident apertures 12aand 24a in the waveguide 12 and resonant cavity 24 respectively. A metalcup 30 is mounted on the cavity 24 and has a ferrite rod 34 extendingfrom the interior to the cavity 24 into the interior of the metal cup 30through an aperture 38, the metal cup 30 and aperture 38 being locatedso that the ferrite rod 34 couples at a position of maximum magneticfield. A coil 36 surrounds the metal cup 30 and is connected to avariable current source comprising a battery 40 and a current controlpotentiometer 42.

A change in the current flowing through the coil 36 changes the magneticfield applied to the ferrite rod 34 and causes a change in the resonantfrequency of the resonant cavity 24. A change in the resonant frequencyof the resonant cavity 24 alters the impedance presented to thewaveguide 12 at its aperture 12a, producing a change in the microwavelength between the radiators 20a and 20b and resulting in a change inthe relative phase between the energy radiated by the radiators 20a and20b. The relative phase shift obtained between the radiators 20a and 20bis equivalent to that produced by applying the same magnetic field to amuch larger piece of ferrite not placed in a resonant cavity. Relativephase shifts considerably higher than previously obtainable are nowpossible.

Figures 2a and 2b show views of a cavity-fed linear array havinginternal microwave cavity means for electrically varying the phase ofenergy radiated by the radiators relative to one another, in accordancewith the invention. A resonant T E mode cavity 44 is divided into sixelementary resonant cavities 50a, 50b, 50c, 50d, 50s, and 50 by shortingposts 60a and 60b placed at points of zero electric current and zeroelectric and magnetic fields within the TE mode cavity 44. Center linesdrawn through the shorting posts 60a and 60b parallel to the walls ofthe TE mode cavity indicate the elementary resonant cavities 50a, 50b,50c, 50d, S0e, and 50f. Microwave energy is supplied to the TE modecavity 44 through an aperture 46. Two ferrite radiating elements 20a and20b are placed to form a linear array and are coupled to the energy inthe TE cavity 44 in accnrdance with well known practice.

A metal cup 30 is mounted on the TE mode cavity 44, and a ferrite rod 34extends from the interior of the TE mode cavity 44 into the interior ofthe metal cup 30 through an aperture 38. The metal cup 30 and aperture38 are located so that the ferrite rod 34 couples to the elementaryr'esonant cavities 50 c and 50 at a positionof maximummagnetic field. Acoil 36-surrounds the metateu so andis connected to a variable currentsource; comprisinga battery 40- and a current control potentiometer 42."

Achange inthe current flowing through the coil 36 changes the magneticfield applied to the ferrite rod 34 and-causesa change-in ;the resonantfrequency ofthe elementary resonant cavities 50cand 50f-to which theferrite rod 34 is coupled. A change in the resonant frequencyofthe-elementary resonantcavity 50c changes the microwave length appearingbetween the radiators 20a and 20b and results in a change in therelative phase between the energy radiated by theradiators 20a and zllb.

'1 he cavity-fed array as basically illust-rated in Figures- Za-and 2bhas the advantage that each of theelementary resonant cavities will havethe same energy within the elementary cavity even though the resonantmode cavity is fed at only one place. This advantage of cavity-fedarrays'pennits convenient and simple adjustment of the power radiated byeach radiatingelement. Thisadvantage becomes 'rnore. greatly apparent asthe number of radiating elements is increased. The power radiated byeach radiatorof a waveguide-fed array as basically illustrated in Figurel is more'difficult to adjust because the amplitude andphase of theenergy reaching each radiator will depend upon the amount of energyabsorbed by the previous radiators.

a'IheQ-particu'lar cavity-fed array and cavity control meansof Figures2a and 2b has afurther advantage. Because :t-hefshorting-post-s 60a and60b furnish tight boundary conditions operation in the TE mode cavity 44is restricted to-a single well defined and especially chesen-fcavitymode. =Therefore, even for largechanges induced in-itheelementaryresonant cavities by changes in the magnetic field applied to theferrite rod'34, the mode' of operation within the TE g cavity 44 remainssubstantially the same.

The principles and advantages of the linear cavity-fed array havinginternal microwave" cavity control means asim Figuresla and 2b canbeextended to a rectangular cavity-fed arrayas-shown inFigures 3a andSb.'I-n-Fig- Hres-3a-=and-3baTE p mode cavity 54 is divided into twelve:elementary resonant ca'vities=50a-,-'50 b, 50c, 50d, 50e, -50f, 50g,=50h-, 50i,*50j ,50k, -50lby shorting-posts 60a,60b,-60c;-60d,"60e, andfitlfplaced at points of zero currentandzero electric and magneticfields withinthe 'I-E gmode cavity 54. "Center lines' drawn through theshorting 'posts'fillacand fiflli parallel to the walls-of-the TE modecavity 54' indicate the elementary-resonant cavities-50; Microwaveenergy is supplied to the-TEg mode ca-vity54 through; an aperture 56'.-Four ferrite radiating elements 20a, 20b, 20c, and 20d are placed toform a'arectangular array and are coupled to the TE cavity =5'4inaccordance with well known practice.

Four metal'cups 30a; 30b; '3 c, and 30d, mounted on the TE gpmode cavity54-between the radiatons h'ave ferrite rods 341L341), 3'4c,"'and 34dextending from the interior of 'the TE cavity54 i'nto'the'metal cups30a,30b,='30c, and-"30d through: apertures 38a, 38b, 38c, and 33drespectively, themetalcups'30'and apertures- 38 being placed 50* thateach ferrite rod 34- is coupled at' a position of maximum magnetic fieldto an elementary cavity 50 located between apair of radiator-s 20, Coils36a 36b, 36c and36d :surr'oundmetal cups- 30a, 3llb,-3ilc and 30drespectively, each of the coils '36 being connected to its own variable"current-- source comprising a battery 40- 'and a currentcontrolpotentiometer 4 2.

The operation of the rectangular cavity-fed array'having internalmicrowave cavity control means as in Figures Ba and 3'b ';issubstantially the as the: opera;

tion of the linear cavity-fed array of Figures 2a and 2b.

That is, by varying the current'through the coils 36, the

phases between the energy radiated by the radiators 20 may be variedrelative to-one another. Skilled persons will be ahleto provide variousequivalents of the current control 'rn comprising batteries 5 As anapotentiometers 42 that-w1ll permit-the mauve phases to be varied inaccordancewith anydesired pe iodic or aperiodic program; a d'atvery highrates of -speed.

. =The cavity fed rectangular array of Figures 4a and 4b illustrates theus'e of external cavity control means for varying the phases between theenergly radia't'ed by the radiators relative to oneanother. In Figures4a and 4b a TE mode cavity 64 isdivid'edinto eight elementary resonantcavities 502z;50b,- 50c, 50d;50e, 501, 50g, and 50h by amicrowavestructure 70 symmetrically located at the center of the'TE modecavity 64. The microwave'structure '-70 eo mprises two resonant cavities70a and 70b havingcoupling i-rises 65 and 65b. Four ferrite radiators 20a," 20b,20 c, and ztld are coupled to elementary cavities 50a, 50g,50:: and 500 respectivelyto form'a rectangular-array in accordance withwell known practice, Mi'crowave energy is supplied to the TE modecavity; throughan aperture 66. Metal cups 30a;-and 30b, mounted oncavities 70a and 70b respectively, have ferrite rods 34a and 34b ex;tendingfrom the interior of the "LE cavity 64 through apertures isaand-3811 respectively. Coils fi a and 36 b surround metal cups 30a and30b respecthiely, each of the coils 36a-and 36b being connected tovariable current sources comprising' a battery 40a and potentiometer 42aforthe coil -36a an'd a battery 4% and potentiometer 42b. for the coil36b.

By changingthe current applied' to coil36a, a changeintheresonantfrequency-of cavity 70a is effected causing achange in thernicrowave length between the two radiators zllw and :20b and the tworadiators 20d and 200. change-imthe current applied to coil 36b effectsasimilarchange i-n the resonant frequency of cavity 'l-llbrpermittingcontrol of the microwave length between the twomadiators zoa and 20c,and the two radiators 20b and 20d. This type of rectangulararray hasthe, advantage over the rectangular array of Figures 3a and 3bof-allowingcontrol ofthe microwave length between two. pairs ofradiators'by-a sing-le' reson ant cavity. 7)

Thedilference between-the external and internal cavity means forcontrolling the microwave length is that in the internal case, controlof microwave length is obtained cont-rolling -;th'e resonantfreguency-of one of the elementary resonant cavities-forming part ofthereson'ant cavity structure while'in the external case control ofmicro wave length is obtained by controlling the resonant frequency--of- 'an external resonant cavity coupled to the resonantcavitystructure 'at the place where the change in microwave length isdesired. Since the external cavity can be'eoupled-at a number 7 ofplaces to the same" resonant cavity structure or toj-difierent cavitystructures, a greater versatility can be obtained.

;Although;th e linear afidrectan'gular arrays have been cavitystructure; means for dividing said resonant cavity into elementaryresonant cavities; two radiators placed on said resonant cavitystructure to form a linear array; a metal cup mounted on said resonantcavity structure between said radiators; a ferrite rod extending fromthe interior of said resonant cavity structure through an aperture intothe interior of said metal cup, said aperture and said metal cup beingplaced so that said ferrite rod is coupled to an elementary cavitylocated between said radiators; a coil surrounding said metal cup; andmeans for applying a variable current to said coil thereby varying thephases between the energy radiated by said radiators relative to oneanother.

2. A rectangular, mechanically stationary microwave antenna array thebeam of which may be varied electrically, comprising in combination: aresonant cavity; means for supplying microwave energy to said resonantcavity; means for dividing said resonant cavity into elementarycavities; four radiators placed on said resonant cavity structure toform a rectangular array; four metal cups mounted on said resonantcavity structure, one metal cup being mounted between each pair ofradiators; four ferrite rods, each rod extending from the interior ofsaid resonant cavity structure through an aperture into the interior ofone of said metal cups, said metal cups and apertures being placed sothat each ferrite rod is coupled to an elementary cavity located betweena pair of radiators; a coil surrounding each metal cup; and means forapplying a variable current to each of said coils thereby varying thephase between the energy radiated by said radiators relative to oneanother.

3. A mechanically stationary microwave antenna array the beam of whichmay be varied electrically, comprising in combination: a resonant cavitymicrowave structure; means for supplying microwave energy to saidmicrowave structure; radiators coupled to said microwave structure; andmicrowave cavity means for electrically varying the microwave lengthbetween said radiators so that the phases between the energy radiated bysaid radiators are varied relative to one another, said microwave cavitymeans for varying the microwave length between said radiators comprisingmeans for dividing said resonant cavity into elementary resonantcavities, and electrically controlled means for varying the resonantfrequencies of predetermined elementary resonant cavities, saidpredetermined elementary cavities being chosen between said radiators sothat variations in the resonant frequencies of said predeterminedelementary cavities varies the phases between the energy radiated bysaid radiators relative to one another.

5 4. The invention in accordance with claim 3 wherein said means fordividing said resonant cavity structure into elementary resonantcavities comprises: shorting posts placed at points of zero electriccurrent and zero electric and magnetic fields within said resonantcavity.

10 5. The invention in accordance with claim 3 wherein the resonantfrequency of each predetermined elementary resonant cavity is varied byelectrically controlled means comprising: a ferrite piece coupled tosaid predetermined elementary cavity; and electrically controlled meansfor applying a variable magnetic field to said ferrite piece.

6. The invention in accordance with claim 3 wherein the resonantfrequency of each predetermined elementary resonant cavity is varied byelectrically controlled means comprising: a metal cup mounted over saidpredetermined elementary cavity; a ferrite rod extending from theinterior of said predetermined elementary cavity through an apertureinto the interior of said metal cup; and electrically controlled meansfor applying a variable magnetic field to said ferrite rod.

7. The invention in accordance with claim 5 wherein said electricallycontrolled means for applying a variable magnetic field to said ferriterod comprises: a coil surrounding said metal cup; and means for applyinga variable current to said coil.

8. The invention in accordance with claim 7 wherein said means fordividing said resonant cavity structure into elementary resonantcavities comprises: shorting posts placed at points of zero electriccurrent and zero electric and magnetic fields within said resonantcavity.

References Cited in the file of this patent UNITED STATES PATENTS2,645,758 Van De Lindt July 14, 1953 2,728,050 Van De Lindt Dec. 20,1955 2,808,584 Koch Oct. 1, 1957 OTHER REFERENCES Ferrod RadiatorSystems (Reggia et al.), published in IRE Convention Record, part 1,(pp. 213-224), Mar.

